rfc905.txt

RFC 的详细文档！

        a)  concatenation and separation;

        b)  segmenting and reassembling;

        c)  multiplexing and demultiplexing;

        d)  splitting and recombining;

        e)  flow control.




     3.2

     For the purpose of this  International  Standard,  the  following
     definitions apply:










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     3.2.1  equipment:

     Hardware or software or a combination of both;  it  need  not  be
     physically distinct within a computer system.




     3.2.2  transport service user:

     An abstract representation of  the  totality  of  those  entities
     within a single system that make use of the transport service.




     3.2.3  network service provider:

     An abstract machine that models  the  totality  of  the  entities
     providing the network service, as viewed by a transport entity.




     3.2.4  local matter:

     A decision made by  a  system  concerning  its  behavior  in  the
     Transport  Layer  that is not subject to the requirements of this
     protocol.




     3.2.5  initiator:

     A transport entity that initiates a CR TPDU.










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     3.2.6  responder:

     A transport entity with whom an initiator wishes to  establish  a
     transport connection.

     NOTE - Initiator and responder are  defined  with  respect  to  a
     single  transport  connection.  A transport entity can be both an
     initiator and responder simultaneously.




     3.2.7  sending transport entity:

     A transport entity that sends a given TPDU.




     3.2.8  receiving transport entity:

     A transport entity that receives a given TPDU.




     3.2.9  preferred class:

     The protocol class that the initiator indicates in a CR  TPDU  as
     its first choice for use over the transport connection.




     3.2.10  alternative class:

     A protocol class that the initiator indicates in a CR TPDU as  an
     alternative choice for use over the transport connection.








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     3.2.11  proposed class:

     A preferred class or an alternative class.




     3.2.12  selected class:

     The protocol class that the responder indicates in a CC TPDU that
     it has chosen for use over the transport connection.




     3.2.13  proposed parameter:

     The value for a parameter that the initiator indicates  in  a  CR
     TPDU that it wishes to use over the transport connection.




     3.2.14  selected parameter:

     The value for a parameter that the responder indicates  in  a  CC
     TPDU that it has chosen for use over the transport connection.




     3.2.15  error indication:

     An N-RESET indication,  or  an  N-DISCONNECT  indication  with  a
     reason code indicating an error, that a transport entity receives
     from the NS-provider.










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     3.2.16  invalid TPDU:

     A TPDU that  does  not  comply  with  the  requirements  of  this
     International Standard for structure and encoding.




     3.2.17  protocol error:

     A TPDU whose use does not comply  with  the  procedures  for  the
     class.




     3.2.18  sequence number:

        a)  The number  in  the  TPDU-NR  field  of  a  DT  TPDU  that
            indicates  the  order in which the DT TPDU was transmitted
            by a transport entity.

        b)  The number in the YR-TU-NR field of an AK or RJ TPDU  that
            indicates the sequence number of the next DT TPDU expected
            to be received by a transport entity.




     3.2.19  transmit window:

     The set of consecutive sequence numbers which a transport  entity
     has been authorized by its peer entity to send at a given time on
     a given transport connection.












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     3.2.20  lower window edge:

     The lowest sequence number in a transmit window.




     3.2.21  upper window edge:

     The sequence  number  which  is  one  greater  than  the  highest
     sequence number in the transmit window.




     3.2.22  upper window edge allocated to the peer entity:

     The value that a transport entity communicates to its peer entity
     to be interpreted as its new upper window edge.




     3.2.23  closed window:

     A transmit window that contains no sequence number.




     3.2.24  window information:

     Information contained in a TPDU relating to  the  upper  and  the
     lower window edges.












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     3.2.25  frozen reference:

     A reference that is not available for assignment to a  connection
     because of the requirements of 6.18.




     3.2.26  unassigned reference:

     A reference that is neither currently in use  for  identifying  a
     transport connection or which is in a frozen state.




     3.2.27  transparent (data):

     TS-user  data  that  is  transferred  intact  between   transport
     entities  and  which  is  unavailable  for  use  by the transport
     entities.




     3.2.28  owner (of a network connection):

     The transport entity that issued the N-CONNECT request leading to
     the creation of that network connection.




     3.2.29  retained TPDU:

     A TPDU  that  is  subject  to  the  retransmission  procedure  or
     retention  until  acknowledgement  procedure and is available for
     possible retransmission.








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     4  SYMBOLS AND ABBREVIATIONS

     4.1  Data units

        TPDU          Transport protocol data unit
        TSDU          Transport service data unit
        NSDU          Network service data unit




     4.2  Types of transport protocol data units

        CR TPDU          Connection request TPDU
        CC TPDU          Connection confirm TPDU
        DR TPDU          Disconnect request TPDU
        DC TPDU          Disconnect confirm TPDU
        DT TPDU          Data TPDU
        ED TPDU          Expedited data TPDU
        AK TPDU          Data acknowledge TPDU
        EA TPDU          Expedited acknowledge TPDU
        RJ TPDU          Reject TPDU
        ER TPDU          Error TPDU




     4.3  TPDU fields

        LI               Length indicator (field)
        CDT              Credit (field)
        TSAP-ID          Transport service access point
                         identifier (field)
        DST-REF          Destination reference (field)
        SRC-REF          Source reference (field)
        EOT              End of TSDU mark
        TPDU-NR          DT TPDU number (field)
        ED-TPDU-NR       ED TPDU number (field)
        YR-TU-NR         Sequence number response (field)
        YR-EDTU-NR       ED TPDU number response (field)






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     4.4  Times and associated variables

        T1               Elapsed time between retransmissions
        N                The maximum number of transmissions
        L                Bound on reference